Optical filter and method of manufacture



April 194& E. R. BLOUT ETAL. 2,440,070

OPTICAL FILTER AND METHOD OF MANUFACTURE Filed Oct. 28; 1944 {Cellulose Acelale ,7 Conlqining Cinnarnalazinc IG. 2 F 3.0

Wavelenglh in Millimicrons F IG- 3 v Wavelenglh in Millimicrons INVENTORS 5x45 IMW-WAL Patented Apr. 20, 1948 OPTICAL FILTER AND METHOD OF MANUF CTUR Elkan R. Blout, Cambridge, and Ralph M. Gofstein, Haverl ill, Masa, asslgnors to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Application October 28, 1944, Serial No. 560,800

15 Claims.

This invention relates to light-filtering materials, and more particularly to a new and improved light-filtering material substantially absorbing ultra violet radiation but substantially transmitting visible light.

It is a particular object of the present inventlon to provide ultra violet absorbin material having high extinction for ultra violet radiation as well as high stability thereto and which particularly will not fluoresce when exposed to ultra violet radiation.

A further object is to provide such ultra violet absorbing material in the form of a transparent carrier agent, either solid or liquid, having incorporated therein a selectively light-absorbing agent comprising an aromatic azine or substituted aromatic azine.

A still further object is to provide ultra violet absorbing material having the above advantages and comprising a sheet of transparent organic plastic material having incorporated therein an aromatic azine or substituted aromatic azine.

A still further object is to provide a process for producing the above ultra violet absorbing materials, and additional objects and advantages will in part appear and in part be pointed out in the course of the following detailed description of several embodiments of the invention,

which are given as nonlimiting examples, in connection with the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a lightfiltering material illustrating an embodiment of the invention;

Figure 2 is a graph illustrating the optical densities of a variety of filters embodying forms of the invention; and V Figure 3 is a graph illustrating the molecular extinction coeflicient of certain of the materials used in the practice of the invention.

In accordance with the present invention, it has been discovered that certain novel and valuable properties with respect to the selective absorption of light rays in the ultra violet region of the spectrum are possessed by the group of compounds which may be generally designated as the aromatic azines and substituted aromatic azines. Said compounds may be represented most simply by the general formula be any aromatic group or condensed aromatic ring system. Specific examples of some of the i-url'uralazine and clnnamaiazine The present invention is directed to taking advantage of the ultra violet absorbing properties of the above compounds by incorporating them in suitable carriers in such manner that they may readily be used as light filters. For example, such a filter may be produced by incorporating one of said compounds in a sheet of transparent organic plastic, as illustrated at ill in Fig. 1. In preparing such light-filtering material, the first step is to prepare the desired azine, which may be done conveniently from the corresponding aromatic aldehyde or ketone.

Cinnamalazine has been found particularly useful for the purposes of the invention and will accordingly be used as an illustrative example of one embodiment thereof. Said compound may be conveniently prepared by shaking together 2.3 mols of cinnamaldehyde with 1 mol of hydrazine hydrate in water or dilute ethyl alcohol and, if desired, purifying the resulting precipitate by recrystallization irom ethanol or any other suitable solvent. The incorporation of the azine in the desired plastic carrier may be done conveniently by forming a solution of both materials ln a suitable mutual solvent, casting or otherwise treating the solution to dorm a. sheet and driving oil the solvent. If, for example, the plastic is cellulose acetate, a suitable solvent will be ethyl acetate or a mixture of ethyl acetate and methanol. The optical density of the resulting sheet will depend upon both its thickness and the concentration of azine therein. For example, curve 20 in Fig. 2 illustrates the optical density of a sheet of cellulose acetate approximately 0.0040 inch in thickness and containing approximately 1% by weight of cinnamalazine. It will be noted that said curve illustrates a very sharp cut-oil at approximately the boundary between the violet and the ultra violet, rising almost vertically between approximately 400 and 410 mg to a value of the order of 2.0 at 400 m This means that its transmission is only 1% at 400 m and for shorter wavelengths the density is so high as to be impractical to measure and the absorption may be considered as substantially total.

The other curves in Fig. 2 illustrate the densities of other examples of the invention. In the case of curves 22 and 24, the absorbing agent is respectively 2% by weight of benzaiazine and 1% by weight of furfuralazine. Curve '25 illustrates the corresponding properties of such a filter wherein the absorbing agent comprises 1% by weight of 1,1'-naphthalazine All of said azines may be prepared in the same manner as already described in connection with cinnamalazine by reaction between the corresponding aldehyde and hydrazine. The recrystallization solvent for benzaiazine may comprise pyridine and for the other two may comprise ethanol. In each case the carrier for the azine is cellulose acetate approximately 0.0040 inch in thickness. All of these examples of embodiments of the invention have highly desirable properties as ultra violet absorbing filters. The sharp cut-offs obtainable with said materials, as well as their high absorption of ultra violet radiation, are clearly illustrated by the curves in Fig. 2.

In addition they are highly stable to ultra violet light, and they have also the unusual and highly valuable property of nonfluorescence in ultra violet light.

In accordance with the invention it has also been discovered that the same and still further advantages as ultra violet absorbers are possessed by the substituted members of the above class, which may be represented by the general formula wherein R" represents any substituent which can be substituted for hydrogen, such for example as an alkyl or aryl radical, a halogen, a nitro, hydroxyl or amino group, or the like, and the other symbols have the same meanings as given in connection with the first general formula hereinabove. In particular, it appears that the shape and position of the absorption curves of said substituted compounds may be to a'considerable extent controlled by the selection both of the substituent and of the position substituted. This may be conveniently illustrated by considering a series of such substitution compounds, for example, the hydroxy-substituted benzalazines.

Curve 30 in Fig. 3 illustrates the molecular extinction coemcient (log e) of benzaiazine as derived from the equation wherein d is the optical density, c is the concenpound shows the broadest absorption band without sharp peaks. The o-substituted compound is characterized by two peaks, one at approximately 295 my and the other at approximately 355 m. The p-substituted compound is characterized by the highest and sharpest peak as well as by its sharp cut-oft. In fact, p-dihydroxybenzaiazine has a curve very nearly parallel to that of benzaiazine except that its cut-off is even sharper at the longest absorbed wavelengths.

The spectral characteristics illustrated by Fig. 3 will be found to hold generally true for other isomeric substituted azines of the class with which the present invention is concerned. It will be apparent therefore that the appropriate substitution compound mayreadilybe chosen to give any particular desired absorption-characteristics with respect to breadth, spectral location and cut-off. In each case the substituted compounds absorb at longer wavelengths than the unsubstituted, but the difference between the two cut-offs may be controlled by choice of the substituted substituents. Thus if the substituted group is one tending to give up electrons to the aromatic ring, for example a hydroxyl or methoxyl group, the shift of the absorption curve towards the red end of the spectrum is much greater than when the substituted group is one tending to draw electrons from the ring, for example a nitro group.

The present invention is applicable to a wide variety of materials, both as to the absorbing agent and as to the carrier therefor. No theoretical limits have been found as to the absorbing agent provided it conforms with the above general structural formulae. Examples of some varied compounds wherein R is other than hydrogen include acetophenoneazine benzophenoneazine and fluorenoneazine C=NN=C' It appears that the substitutions on the ring may be at any position and may comprise any substituent which can be substituted for hydrogen, may be at more than one position, and in the latter case may be the same or difierent. This may be expressed in a general formula for the case of benzene compounds by modifying the second above general formula to Wherein R" may be at any one or more positions on the ring and represents any one or more substituents which can be substituted for hydrozen. All these compounds may be readily prepared from the corresponding aromatic aldehyde )1 ketone by reaction as described above with iydrazine. In some cases the hydrazone may form, but it can readily be decomposed to the azlne by adding to the recrystallization solution a. drop of an acid such as hydrochloric acid. Eximples of some such varied compounds found lseiul in the practice of the invention include, n addition to those already given, the azlnes of ;he isomeric aminobenzaldehydes, nitrobenzaldeaydes, methoxybenzaldehydes, ethoxybenzaldeiydes, dimethylaminobenzaldehydes and isopropylbenzaldehydes. It is to be understood, iowever, that this list is given merely as illus- ;rative of some of the compounds coming within ahe scope of the invention.

A wide variety of carrier agents may be used for the selectively light-absorbingagents oi the .nvention. In addition to the cellulose acetate already mentioned, other suitable cellulosic plas- ;ics include cellulose nitrate and cellulose aceate butyrate. Polyamide plastics of the nylon type may also be used as well as vinyl compounds ;uch as polyvinyl alcohol. It will be apparent ;hat choice of the carrier agent will depend partly on the conditions under which the filters will be used and also will be limited to the ex- ;ent that the carrier and absorbing agent should ae soluble in a mutual solvent. In the case of water soluble plastics such as polyvinyl alcohol ahe azlne may be incorporated therein by first forming a water soluble azlne salt such for example as the disodium salt in the case of hyiroxy-substituted compounds and the hydro- :hloride in the case of the amino compounds. It will be apparent that the use of such carrier is limited to such of the azines as will form water soluble salts without alteration of their absorp- ;ion characteristics. It will also be apparent that the azines of the invention may be used in liquid solution, although the practicability of such use may be limited. 4

It will also be apparent that the plastic lightflltering material of the invention may readily be provided with any suitable protective means. For example, the sheets of cellulose acetate described hereinabove may be bonded between additional thicker and clear layers of cellulose acetate by means of any suitable solvent such as acetone, or may be bonded between layers of glass by any suitable adhesive such as an incomplete polyvinyl acetal resin plasticized with raw castor oil. Other such modifications oi the invention will be readily apparent to those skilled in the art and are to be construed as coming within the scope hereof.

Since certain changes in carrying out the above process, and certain modifications in the product which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description, or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a light-transmitting carrier having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one. It represents a member of the class consisting of hydrogen and alkyl and aryl radicals, and R represents a member of the class consisting of aromatic hydrocarbon rings, condensed aromatic hydrocarbon ring systems, aromatic oxygen-containing heterocyclic rings and condensed aromatic oxygen-containing heterocyclic ring systems.

2. As a new product. a light-filtering material adapted to absorb ultra violet radiation, said material. comprisinga light-transmitting carrier having incorporated therein a compound oi the general formula wherein n is selected from the group consisting of zero and one, It represents a member of the class consisting of hydrogen and alkyl and aryl radicals, R represents a member of the class consisting of aromatic hydrocarbon rings, condensed aromatic hydrocarbon ring systems. aromatic oxygen-containing heterocyclic rings and condensed aromatic oxygen-containing heterocyclic ring systems, and R" represents at least one substituent from the class consisting of alkyl and aryl radicals and halogen, nitro, hydroxyl and amino groups.

3. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising light-transmitting carrier having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one. and R represents a member of the class consisting of hydrogen and alkyl and aryl radicals.

4. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a light-transmitting carrier having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one, B represents a member of the class consisting of hydrogen and allwl and aryl groups, and R" is in any position on the benzene ring and represents at least one substituent from the class consisting of alkyl and aryl radicals and halogen, nitro, hydroxyl and amino groups.

5. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a sheet or light-transmitting organic plastic material having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one, R. represents a member of the class consisting of hydrogen and alkyl and aryl radicals, and R represents a member of the class consisting of aromatic hydrocarbon rings, condensed aromatic hydrocarbon ring systems, aromatic oxygen-containing heterocyclic rings and condensed aromatic oxygen-containing heterocyclic ring systems.

6. As a new product, a light-filtering material adapted to absorb ultra violet'radiation, said material comprising a sheet of light-transmitting organic plastic material having incorporated therein a compound of the' general formula wherein n is selected from the group consisting of zero and one, R represents a member of the class consisting of hydrogen and alkyl and aryl radicals, R represents a member of the class consisting of aromatic hydrocarbon rings, condensed aromatic hydrocarbon ring systems, aromatic oxygen-containing heterocyclic rings and condensed aromatic oxygen-containing heterocyclic ring systems, and R" represents at least one substituent from the class consisting of alkyl and aryl radicals and halogen, nitro, hydroxyl and amino groups.

7. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a sheet of light-transmitting organic plastic material having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one, B. represents a member of the class consisting of hydrogen and alkyl and aryl radicals, and R" is a substituent selected from the class consisting of alkyl and aryl radicals, halogen, nitro, hydroxyl and amino groups. I 9. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising. a sheet of light-transmitting organic plastic material having incorporated therein a compound of .the general formula wherein n is selected from the group consisting of zero and one, R represents a member of the class consisting of hydrogen and alkyl and aryl radicals, and R" is a substituent selected from the class consisting of alkyl and aryl radicals, halogen, nitro, hydroxyl and amino groups.

10. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a sheet of light-transmitting organic plastic material having incorporatel therein a compound of the general formula wherein n is selected from the group consistinl of zero and one, R represents a member of thl class consisting of hydrogen and alkyl and ary radicals, and R" is a substituent selected iron the class consisting of alkyl and aryl radicals halogen, nitro, hydroxyl and amino groups.

11. As a' new product, a light-filtering materia adapted to absorb ultra violet radiation, saic material comprising a sheet of light-transmittim cellulosic plastic material having incorporate therein a compound of the general formula wherein n is selected from the group consisting of zero and one, R represents a member of th class consisting of hydrogen and alkyl and ary radicals, and R' represents a member of the clas consisting of aromatic hydrocarbon rings, condensed aromatic hydrocarbon ring systems, aromatic oxygen-containing heterocyclic rings ant condensed aromatic oxygen-containing heterocyclic ring systems.

12. As a new product, a light-filtering materia adapted to absorb ultra violet radiation, said material comprising a sheet of light-transmittini plastic material comprising cellulose acetate, saic sheet having incorporated therein a compound 01 the general formula wherein n is selected from the group consisting of zero and one, R represents a member of the class consisting of hydrogen and alkyl and aryl radicals, and R represents a member of the class consisting of aromatic hydrocarbon rings condensed aromatic hydrocarbon ring systems aromatic oxygen-containing heterocyclic ring: and condensed aromatic oxygen-containing heterocyclic ring systems.

13. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a sheet of light-transmitting plastic material comprising cellulose acetate, said sheet having incorporated therein a compound of the general formula wherein n is selected from the group consisting of zero and one, R represents a member oi. the class consisting of hydrogen and alkyl and aryl groups, and R" is in any position on the benzene ring and represents at least one substituent from the class consisting of alkyl and aryl radicals and halogen, nitro, hydroxyl and amino groups.

14. As a new product, a light-filtering material adapted to absorb ultra violet radiation, said material comprising a sheet of light-transmitting plastic material comprising cellulose acetate and having incorporated therein a selectively lightabsorbing agent comprising cinnamalazine.

15. In a process of forming light-filtering material substantially absorbing ultra violet radia- 9 a 10 tion. the steps comprising forming a mutual sol. vent a solution comprising a light-transmitting REFERENCES mm organic plastic materlal and a compound com- The following references are .of record in the prising clnnamalazine, and then casting said solufile of this patent: tion to form a sheet, and substantially removing 5 the solvent from said sheet. UNITED STATES PATENTS Number Name Date ELKAN R. BLOUT- 2,298,733 Brooker 8i, 8]. Oct. 13, 1942 RALPH M- coFs 2,340,882 Kendall Fb. 8, 1944 Certificate of Correction Patent No. 2,440,070 April 20,1948 ELKAN R. BLOUT ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requirmg correction as follows:

Column 3, line 73, for unsusbstituted read unsubstituted; column 7, line 39, for porduct read product; column 9, line 1, after the word forming insert in;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 29th day of August, A. D. 1950.

THOMAS F. MURPHY,

Assistant 00mm of Patents. 

